David Cameron casually hummed as he stepped away from one of his last announcements as Prime Minister

There has been some speculation that Cameron was humming the end of the theme from hit US TV drama The West Wing, which follows the career of a fictional Democratic president and his advisers in the White House.

The audio of Cameron casually singing was picked up by an ITV microphone as he walked back into 10 Downing Street.

He is also heard saying "right" as the famous door closes behind him.

David Cameron this afternoon made a short statement that current Home Secretary Theresa May will be his successor, with May to take over by the end of the week.

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In making the announcement, Cameron said he was "delighted" that May would succeed him.

He said: "She is a strong, she is competent, she is more than able to provide the leadership that our country is going to need in the years ahead and she will have my full support."

He said he would go to the Palace to offer his recognition to the Queen on Wednesday afternoon.

Cameron will chair his last Cabinet meeting tomorrow morning and appear in the Commons for the final time as premier when he takes to the Despatch Box for Prime Minister's Questions at noon on Wednesday.

He announced he would leave the top job after the Brexit referendum which saw an overwhelming vote for Britain to leave the EU, despite Cameron having encouraged Britain to remain.